RU2566140C1 - Magnetic nanostructure powder of particles of system iron-cobalt-nickel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to magnetic powder of system Fe-Co-Ni. The magnetic nanostructure powder of the particles of the system iron-cobalt-nickel is characterised in that each powder particle contains in wt %: nickel 10-20, cobalt 10-50, iron - rest, at that contains nanocrystallites with size below 20 nm, compactly arranged in aggregates with size from 40 to 80 nm with creation of the agglomerates having spherical shape with size from 100 to 200 nm.

EFFECT: powder is characterised with high magnetic properties.

7 dwg, 1 tbl, 1 ex

Description

The invention relates to the production of magnetic powder, in particular to a magnetic system consisting of iron, cobalt and nickel (Fe-Co-Ni). This system can be used to create new magnetic materials from it or on its basis, for example, for use in information recording and storage systems, in the manufacture of miniature magnets, magnetic suspensions, and also as a radar absorbing material.

Currently, magnetic nanopowders of individual metals are obtained mainly in two groups of methods: chemical, based on the deposition with subsequent reduction or thermal decomposition of metal oxides or hydroxides, and physical, most often including the evaporation of the metal and its subsequent condensation or mechanical disaggregation of large (macro ) samples. These production methods have disadvantages:

high energy intensity, relatively low magnetic characteristics of the products, the possibility of contamination of the powder with diamagnetic impurities, the instability of the magnetic properties with increasing temperature, which generally affects their performance.

Known powder (patent RU 2427451, IPC B22F 9/04, B82B 3/00, publ. 08/27/2011) obtained by preliminary heat treatment of the selected starting material in the form of an amorphous ribbon of soft magnetic alloys based on the Fe-Co-Ni system at a temperature equal to (0.25-0.29) -T _liquidus for 30-90 minutes with cooling in air and preliminary grinding of the heat-treated tape to a fraction of 3-5 mm. Then grinding is carried out in a high-speed disintegrator due to particle collision to obtain an amorphous structure powder with a fraction size of 20-60 microns. The final heat treatment of the obtained amorphous powder is carried out at a temperature equal to (0.3-0.4) -T of _liquidus for 30-90 minutes with cooling in air to create a nanostructure in the bulk of the powder and to isolate nanocrystallites in an amorphous matrix. This powder has several disadvantages: a complex multi-stage production technology with high energy consumption, and the resulting product is composed of large particles with complex chemical and phase compositions.

Fe-Co-Ni magnetic fibers are known (Ji Hea Park, Soon C. Kweon, Sang Woo Kirn. Structural and magnetic properties of electrospun FeCoNi magnetic nanofibers with nanogranular phases / Journal of Nanoparticle Research, January 2012, 14: 729) size 10 × 100 nm. The disadvantages of this material are: complex phase composition, pollution with a large amount of oxygen and, as a result, insufficiently high magnetic characteristics (σ = 160-180 G · cm ³ / g), changing under the influence of temperature.

Magnetic powder Fe-Co-Ni is known (Zhang Chao-ping, Lei Bing-xin, Li Zhen. Preparation and Magnetic Properties of Nanosize FeCoNi Alloy and Composite Particles by WaterinOil Microemulsions / Nanotechnology and Precision Engineering, Jan 2012, Vol. 10, No. 1, P.36-44) obtained by reduction with borohydride from a water-oil suspension of salts.

The disadvantages of this material are: complex phase composition, the presence of intermetallic compounds, oxides, pollution with large quantities of oxygen and boron, as a result, the powder has insufficiently high magnetic characteristics, consists of large nanoparticles (more than 20 nm).

Closest to the claimed invention is magnetic powder Fe-Co-Ni (article by N.F. Kushchevskaya et al. Magnetic Fe-Co-Ni nanoparticles obtained by reduction from a mixture of oxalates / Report of the national academy of sciences of Ukraine, 2007, No. 11, P.93-98), in which Fe-Co-Ni thermochemical powders were obtained by reducing a mixture of Fe, Co, and Ni oxalates with a component ratio of 60, 30, and 10% (mass fraction), respectively, in a special carbon-containing medium by carrying out the process in the "gaseous reducing medium-solid" mode.

The disadvantages of this powder are:

- the complex phase composition of the target product (a mixture of α and γ phases of Fe-Co-Ni, or α phase and Fe ₃ O ₄ );

- large particles (3-10 microns);

- insufficiently high magnetic characteristics, which vary depending on temperature (σ = 100-150 G · cm ³ / g). The objective of the invention is to increase the magnetic properties of the nanostructured powder of particles of the Fe-Co-Ni system.

The problem is solved by obtaining a magnetic nanostructured powder of particles of the iron-cobalt-nickel system, characterized in that each powder particle contains, mass. %: nickel 10-20, cobalt 10-50, iron - the rest, while it consists of nanocrystallites with sizes less than 20 nm, compactly folded into aggregates with sizes from 40 to 80 nm with the formation of spherical agglomerates with sizes from 100 to 200 nm.

A method of producing magnetic nanostructured powder of agglomerates of the Fe-Co-Ni system is carried out by the interaction of precursors, which are used as aqueous solutions of salts of iron, cobalt and nickel in the form of chlorides, sulfates or nitrates. Their mixture interacts with reagents at elevated temperatures (up to 85-90 ° C). As reagents, a reducing agent is used - hydrazine hydrate and alkali.

When implementing the method, the obtained Fe-Co-Ni powder has high purity — the total content of foreign impurities is not more than 0.1 mass percent of the powder sample (Fig. 1). The selected production method has several advantages: it is easily scalable, it allows to reduce the cost of the resulting product due to the low energy intensity of the method and the use of inexpensive starting reagents.

The nanostructured iron-cobalt-nickel system is a nanocrystallite with dimensions less than 20 nm (by broadening the diffraction profile - figure 2), compactly folded into aggregates with sizes from 40 to 80 nm (determined from photographs of an atomic force microscope - figure 3), , in turn, low-porous sphere-like agglomerates with sizes from 100 to 200 nm (according to electron microscopic photographs - figure 4). The smaller the particle size, which can be compared with the value of a single magnetic domain for metals (iron - 15 nm, cobalt and nickel - 70 nm), the higher the magnetic characteristics (Figs. 5, 6).

Each component of the agglomerate is a solid solution of Fe-Co-Ni with a body-centered cubic (bcc) lattice, in the nodes of which the atoms of cobalt, nickel and iron alternate, which is determined by analyzing the X-ray diffraction profiles of the system, the position of which corresponds to this crystal structure (Fig. 2) . Reflections of any other crystalline structures are not observed. During X-ray fluorescence and atomic emission spectral analysis of a powder containing nanostructured metal particles, namely iron, cobalt and nickel, are found in quantities corresponding to those contained in the precursors in the synthesis, which also confirms their joint presence in one crystalline phase. Also, the formation of a solid solution is proved from the calculated lattice parameters (Fig. 7), which are laid on straight lines corresponding to isoconcentration slices.

The powder particles have a high density (the measured values of the pycnometric density of 7-8 g / cm ³ ) and are mechanically strong (according to the results of exposure to ultrasound, they do not undergo disaggregation, they do not collapse when pressed - Fig. 3). The specific surface area of the obtained powder, determined by the BET method (Brunauer, Emmett and Taylor method), is about 5-6 m ² / g.

To achieve high magnetic and operational characteristics, Fe, Co, and Ni metals were chosen, since iron-cobalt is a high-magnetic alloy and at the same time cobalt with nickel protects the iron from corrosion.

A method for producing magnetic nanostructured solid-solution powders of iron-cobalt-nickel is implemented as follows: prepare a mixture of salt solutions: m ₁ iron, m ₂ cobalt, m ₃ nickel in 120 ml of distilled water. With continuous stirring on the heating element, the solution was brought to 85-95 ° C. Next, the calculated amount of sodium hydroxide is added to the solution to precipitate the hydroxides of the metals iron, cobalt and nickel. Also, when added, the reducing ability of hydrazine hydrate, which is introduced into the solution further, increases. Constant vigorous stirring is necessary to uniformly form components throughout the reaction volume. After the mixture is kept for 10-15 seconds with constant stirring for the complete precipitation of metal hydroxides. Heating is stopped and the calculated amount of hydrazine hydrate solution is added. The duration of the reaction of recovery is from 10 to 20 minutes Across the entire volume, nanodispersed iron-cobalt-nickel particles are uniformly formed, the formation of which is visually fixed. The more uniform the particles are formed in the volume, the finer the powder. The product yield is 90-95% of theoretical.

When implementing the method, the obtained nanosized powder of Fe-Co-Ni agglomerate particles has high purity - the total mass content of iron, cobalt and nickel according to the results of X-ray fluorescence and atomic emission spectral analyzes reaches 99.9% (Fig. 1).

Figure 1 shows the results of x-ray fluorescence analysis of the elemental composition of the powder, consisting of nanostructured agglomerates of the Fe-Co-Ni system with a composition of 80/10/10 mass. % respectively.

Figure 2 presents a typical diffraction pattern of a nanostructured powder of the Fe-Co-Ni system for a composition of 80/10/10 mass. %, respectively (reflex for bcc structure 111 by 57–58 °, broadening of reflections corresponds to the size of nanocrystallites).

Figure 3 shows an image of a nanostructured compacted powder of Fe-Co-Ni agglomerates obtained using an atomic force microscope for a composition of 40/50/10 mass. % respectively.

Figure 4 presents a raster electronic image of agglomerates of nanopowder Fe-Co-Ni composition 40/50/10 mass. %, respectively (agglomerates with sizes of 100-200 nm).

Figure 5 shows the results of measuring the magnetic characteristics for the composition of Fe-Co-Ni 60/30/10 mass. % respectively.

Figure 6 shows a typical dependence of the saturation magnetization as a function of temperature. A very weak dependence of σ on the temperature of the samples is shown, which is an important operational property of the system.

7 shows the dependence of the lattice parameter of the Fe-Co-Ni system on the cobalt content. The straightforward nature of the relationship indicates the formation of a solid solution.

When analyzing particles of an iron-cobaln-nickel nanopowder using the method of wide-angle radiography (Fig. 2), it was found that the size of nanocrystallites is from 5 to 20 nm (determined by the broadening of diffraction peaks using the Scherrer method). Nanostructured agglomerates of the iron-cobalt-nickel system have spherical structures with a diameter of 100 to 200 nm (Fig. 4). The resulting powder has no impurities and impurities, as shown in figure 1, and is consistent with the data in figure 2. The peak position in FIG. 2 corresponds to the phase of metallic iron, cobalt and nickel with a body-centered cubic lattice, and their broadening indicates the nanocrystalline state of the substance. Individual cobalt has a densely packed hexagonal packing with a maximum of 53 °, which we do not observe in the diffractogram, therefore, this indicates its full integration into a body-centered cubic lattice. Individual nickel has a face-centered cubic lattice with a maximum of 56 °, which is not shown in the diffractogram due to the complete incorporation of nickel into the crystal structure characteristic of iron.

When X-ray fluorescence and atomic emission spectral analysis of a powder containing nanostructured metal agglomerates, namely iron, cobalt and nickel, are detected in an amount corresponding to that incorporated in the synthesis of Fe, Co and Ni precursors, which also confirms their joint presence in one crystalline phase, and their total mass content according to the results of x-ray fluorescence and atomic emission spectral analysis reaches 99.9% (figures 1, 3).

Example 1 (for the composition of the agglomerated system Fe-Co-Ni 50/40/10) the initial reaction mixture contains 4.979 g of iron sulfate heptahydrate, 3.231 g of cobalt chloride hexahydrate, nickel chloride hexahydrate 0.624 g and 120 ml of distilled water with constant stirring with a mechanical stirrer ( 35 rpm). The amount of precursor is calculated on 3 g of pure metal from the ratio of molar mass - a given amount. The prepared solution of metal salts is heated to 85 ° C.

Then, with constant stirring, 30 g of dry sodium hydroxide are added to precipitate the hydroxides of the metals iron, cobalt and nickel.

After stirring for 10-15 seconds, 30 ml of hydrazine hydrate solution is added to the mixture, having previously turned off the heating. The reaction proceeds for 15 minutes with constant stirring, at which time the formation of nanodispersed particles of an iron-cobalt-nickel solid solution is recorded in the entire volume. Next, the mixture is filtered. A black precipitate (nanostructured powder of metal agglomerates) is washed with distilled water and isopropyl alcohol in order to remove possible contaminants by-products. The nanosized powder of iron-cobalt-nickel agglomerates is dried under low vacuum (10 ^-2 mm Hg) in an oven at a temperature of 40-50 ° C for an hour. Store in boxes. The saturation magnetization is 200 G · cm ³ / g.

Other examples of the production of nanosized powder agglomerates of the iron-cobalt-nickel system, performed analogously to example 1, are summarized in table. The examples show a change in magnetic properties with varying composition of the components in the resulting agglomerate.

It was experimentally established that nanostructured metal particles were obtained in the form of a solid solution of the Fe-Co-Ni system, forming agglomerates 100-200 nm in size (against 3-10 microns in the prototype).

The saturation magnetization σ reaches 200 G · cm ³ / g against 100-150 G · cm ³ / g in the prototype.

When implementing the synthesis method, the Fe-Co-Ni powder has high purity — the total content of impurities is not more than 0.1 mass percent of the powder sample.

Advantages of the synthesis method: easy to scale, reduces the cost of the resulting product due to the low energy intensity of the method and the use of low-cost starting reagents, the absence of polluting factors.

Claims (1)

Magnetic nanostructured powder of particles of the iron-cobalt-nickel system, characterized in that each powder particle contains, by weight. %: nickel 10-20, cobalt 10-50, iron the rest, while it consists of nanocrystallites with sizes less than 20 nm, compactly folded into aggregates with sizes from 40 to 80 nm with the formation of spherical agglomerates with sizes from 100 to 200 nm.

Images